This invention concerns a method for production of a sanitary product comprising three interconnected layers, viz. a liquid impervious back sheet, a liquid impervious front sheet, and a liquid pervious core. More specifically the invention concerns a method for producing such product by means of a plant used for making multi-ply paper. The sanitary products in question might be diapers, sanitary napkins and the like.
It is customary to manufacture sanitary products having the liquid impervious back sheet and front sheet made of elastomer sheets and to have the liquid pervious absorbent core comprising a fibrous material interspaced between the front sheet and back sheet. The front sheet and back sheet are sealed along the marginal edge in order to contain the absorbent core in a secure way. In such products it is possible to establish flow lines or flow areas by providing through going holes in the front sheet.
The prior art product would suffer from several drawbacks. As rather narrow sealings are used along the marginal edge there is a risk that the sealing is broken whereby the absorbent core might fall out. There will be a need for correct positioning of the products. A highspeed production of the product is difficult to obtain.
The final product will give the user a poor wearing comfort due to the elastomer front sheet. Moreover, the final product would have a thickness which could be rather large.
It is an object of the present invention to provide a method making it possible to remedy the drawbacks of the prior art methods thereby providing sanitary products giving a high degree of wearing comfort and which are very thin and have a soft and pleasant front sheet for contact with the user.
Moreover, it is an object of the present invention to provide a method making it possible to manufacture the sanitary product in a plant intended for making multi-ply paper. A not limiting example of such plant for dry forming several fibrous layers on a forming surface has been disclosed in U.S. Pat. No. 3,976,412.
According to the present invention a method is provided for the manufacture of the above-mentioned sanitary product wherein the liquid impervious back sheet and front sheet are made of hydrophobic fibers whereas the liquid pervious core is made of hydrophilic fibers, wherein the hydrophobic front sheet is prepared by a striking roller having a pattern of raised ridges whereto a wetting agent is applied for neutralizing the hydrophobicity of the fibers in the hydrophobic front sheet thereby providing a pattern of flow lines being hydrophilic and allowing for a liquid flow through the front sheet.
As the three layers are provided by a fiber laying it is possible to use three successive fiber distributors in a paper manufacturing plant when making the sanitary product. The application of wetting agent according to any pre-selected pattern is easily effected by use of the striking roller.
According to a preferred embodiment it is possible to use an embossing roller as a striking roller. It is customary to have an embossing or pressure roller arranged following the fiber distributors in a plant for dry-laying of paper. Accordingly, only very small modifications are required in the plant
When using an embossing roller it is possible to provide grooves thereby enhancing the wearing comfort of the product as the wetting agent is provided in the bottom of said grooves. Thus a fluid will be directed against the bottom of the grooves and thus in direction of the flow lines. Accordingly, such product would provide a surface for contact with the user which is completely dry due to the hydrophobic fibers in all areas outside the grooves.
Moreover, the use of an embossing roller will compress the fibers in the flow lines. Due to the intimate contact between the hydrophilic fibers in the front sheet and in the core the liquid guidance or the wicking effect becomes more efficient. Thus any liquid would immediately be guided to the absorbent core thereby very quickly leaving the contacting surface of the front sheet dry.
There will be no risk that the individual layers are separated. As the layer is made by following fiber distributors in a paper-making plant the product will have a coherence corresponding to that of multiply papers being manufactured by application of several layers. Thus there will be a bonding between the layers over the total area. Accordingly, it is not necessary to rely on a connection in the marginal area only.
According to a preferred embodiment the embossing roller is manufactured in such a way that the pattern of flow lines are provided in limited areas which are intended for a preselected position in the final sanitary product. Thus it is possible to provide the pattern in an area which is especially suited for the specific sanitary product. Thereby the wearing comfort is enhanced as liquids might be guided through the front sheet in an area of the sanitary product arranged facing against a discharge opening for the body fluid in question.
According to an especially preferred embodiment superabsorbents are admixed to the hydrophilic fibers of the absorbent core. Hereby the absorbing capacity is increased whereby also the wearing comfort is increased. Thus the risk that any fluid will leak out from the absorbent core is obviated even if a large amount of liquid has been absorbed.
According to a further embodiment the superabsorbents are provided only in areas which are intended for a pre-selected position in the final sanitary product. Hereby it is possible to obtain sanitary products being especially suited for different use, e.g. as diapers for boys and diapers for girls.
According to a further embodiment it is possible to spray the penetrant onto the surface of the hydrophobic front sheet by a series of nozzles. However, the use of a striking or embossing roller is preferred. When using nozzles being guided for providing the wetting agent in a pre-selected pattern of flow lines it is possible to use a computer control. This makes it possible to change the production very quickly in order to manufacture sanitary products having different pattern of flow lines. Thus, it will be possible in the same plant to manufacture diapers for boys and diapers for girls without the need of exchanging any mechanical components of the plant.
In general it will be very easy to feed three successive distributors with different types of cellulosic fibers being pre-treated in order to provide hydrophobic fibers and hydrophilic fibers for the different layers.
The fibers to be used in the present invention comprise cellulosic fibers, wood fibers, mixtures with synthetic fibers including bicomponent fibers and synthetic fibers. The synthetic fibers may, e.g., be of polypropylene or polyethylene. Also, glass fibers, rock wood fibers, and pretreated fibers may be used.
Further features and advantages of the present invention will be understood by reference to the attached drawings taken in conjunction with the ensuing discussion.